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Creature information
Scientific name : Basilosaurus isis
Name meaning : King Lizard
Time period : Late Eocene epoch.
Primary diet : Carnivore
In the programmes
Fatalities caused : Two Physogaleus
Several Dorudon
Appearances : Walking With Beasts (New Dawn, Whale Killer)
Sea Monsters (Sea Monsters, Episode 2)
Walking With Cavemen (First Ancestors)
In the books

Basilosaurus was a huge, prehistoric whale that lived in the late Eocene. These were by far the biggest predators in the Eocene seas.


Basilosaurus, just like Dorudon, was a prehistoric whale (Archaeocetii). Over four times the length of a Great White Shark, Basilosaurus was around 18-21 meters in length with a skull approximately 2-3 meters long, and weighed 45-60 tons. Its' post-cranial skeleton resembled that of the modern whales, but it still had nostrils rather than a blowhole, and its' ribcage indicates that it couldn't dive as deep as the modern whales can. Its name is a bit misleading

Incidentially, when it was first discovered in the 1830s and according to a drawing made in 1960, Basilosaurus was thought to have been another giant sea reptile (like a Mosasaur ), just like sea serpents, or even the Loch Ness Monster, and hence its name means "the regal reptile". Later though, via its teeth, Basilosaurus true identity as a primitive whale was established, but due to scientific rules, the original name had to remain.

The skulls of Basilosaurus are chilling to most people. There are no whales with skulls like the skull of Basilosaurus in modern times. Great peg–like teeth at the front for seizing prey. Once inside the mouth, the prey is sliced up by the big teeth at the back, great big cusps at the front: they are for slicing through flesh.

Basilosaurus lived in the late Eocene time period, roughly 43-38 MYA, even though the Walking with Beasts episode is dated 36 MYA instead. It lived in the warm and shallow seas (like the Tethys) of the time, and it resembled the thought carnivorous marine reptiles that died during the K/T extinction event, especially in the skull, where it had saw-edged teeth used for catching fish and other slippery sea life.


Females were eagerly pressured by several males, but it was the eldest and the biggest males the females chose to mate with. Mating was not an easy task for such huge, free–floating animals, so Basilosaurus needed a little extra help. As the successful male maneuvered into position, they called upon one small legacy of their distant lend ancestors. Basilosaurus retained two tiny back legs. These were useless for walking or even swimming, but they were used to lock their long narrow bodies together during mating.

In Walking with... Series

Walking with Beasts

Whale Killer

Basilosaurus was looked up in detail: the audience saw how it used its vestigial hind legs during mating, how it hunted smaller sharks, as well as Dorudon young in the open waters, and how it on occasion would enter the mangrove forests to hunt such creatures as Moeritherium, although unsuccessfully.

Sea Monsters

Sea Monsters, Episode 2

The late Eocene seas in which Basilosaurus lived were identified as the 4th most dangerous sea of all time, mostly because of it. A juvenile 50-footer was attracted by the sounds that came from Nigel Marven's speaker and eventually tore it off and swam away with it, shaking it as a tabby cat would shake a rat.

Walking with Cavemen

First Ancestors

When the continents are moving and the scene goes into the water you can briefly see a Basilosaurus.

Appearances In Other Media

Scribblenauts Series

Read more at the Scribblenauts Wiki

The Scribblenauts series' Basilosaurus looks similar to its appearance in the Walking with... series.


  • In Chased By Sea Monsters, Basilosaurus is depicted being able to 'sing', but in reality, it lacked the organ for this.
  • It more likely hunted adult Dorudon and wasn't that easily driven away by them, considering its size. There is no evidence of adult Dorudon being killed by a Basilosaurus, however, unlike the juveniles.


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